Chip resistant primer composition IV

ABSTRACT

An hydroxy functional epoxy-polyester graft copolymer and solvent-based thermosetting coating composition comprising said copolymer and blocked polyisocyanate crosslinking agent. The coating composition may be formulated as hot sprayable, high solids coating composition suitable for use as chip resistant automotive vehicle primer adapted for use on body panel areas subject to chipping by stones, gravel and other road debris. Alternatively, the composition may be formulated as a high solids composition sprayable with conventional spraying equipment. The hydroxy functional epoxy-polyester graft copolymer is the product of polymerization of certain lactone monomers in the presence of hydroxy functional epoxy amine adduct precursor. The precursor resin is the reaction product of diepoxide with aliphatic diol and, subsequently, with hydroxy functional secondary amine. The polymerization of the lactone monomers is carried out at a temperature between about 50° C. and about 300° C. and the polymerization reaction mixture comprises between about 10 and about 80 weight percent hydroxy functional epoxy amine adduct precursor and between about 90 and about 20 weight percent lactone monomers.

Reference is made to commonly assigned related U.S. application Ser. No.798,044 filed Nov. 14, 1985 entitled "Chip Resistant Primer CompositionI" and Ser. No. 798,079 filed Nov. 14, 1985 entitled "Chip ResistantPrimer Composition I'" and Ser. No. 798,085 filed Nov. 14, 1985 entitled"Chip Resistant Primer Composition I"" and Ser. No. 809,808 filed Dec.16, 1985 entitled "Chip Resistant Primer Composition III", all toKordomenos et al.

TECHNICAL FIELD

This invention relates to a novel hydroxy functional epoxy-polyestergraft copolymer and to a novel, solvent-based, thermosetting coatingcomposition comprising same. It relates also to such coating compositionformulated, for example, as a hot-sprayable, high solids coatingcomposition suitable for use as a chip resistant motor vehicle primeradapted for use on body panel areas subject to chipping by stones,gravel and other road debris.

BACKGROUND

Solvent-based coating compositions are known which can be applied to asubstrate, for example, by spraying, and then cured by baking the coatedsubstrate at an elevated temperature suitable to drive off the organicsolvent and to promote crosslinking reaction. The resulting thermosetcoating, if sufficiently humidity and solvent resistant, can provideaesthetic and functional advantages including corrosion protection forthe underlying substrate.

Automobile manufacturers, in their efforts to extend the expected lifeof automobile sheet metal and the like, have directed considerableattention to various processes and compositions designed to result innot only improved corrosion resistance but also improved chip resistanceproperties. In particular, research and development efforts haverecently been directed to obtaining primer compositions which areflexible and chip resistant and which give corrosion protection whileexhibiting good humidity and solvent resistance, as well as goodintercoat adhesion. New automobile designs and concern about chipping inareas exposed to stones, gravel and other road debris, e.g. rockerpanels, have demanded such chip resistant primers which can be appliedin reasonable thicknesses by techniques which do not require extensiveand expensive process modifications during painting operations. To dateavailable primers, whether high or low solids, have not proven suitable.

In order to overcome the aforementioned chipping problem it has beencommon to apply relatively thick chip resistant coatings in body panelregions which are inclined to chip, prior to application of stillanother primer composition. One such chip resistant sealer materialwhich has been employed is a polyvinyl chloride plastisol sealer whichhas been applied with airless spraygun equipment in thicknesses of about20 mils in regions subject to high levels of chipping. Problemsattendant with such thick coatings are readily apparent. Because of thethickness in the region to which it is applied, these materials presentan appearance problem often resulting in waviness and roughness in thefinal coating on the sheet metal. Often times surface imperfections alsoresult from the fact that a primer is applied over the top of thissealer, with the primer and sealer being cured together. As a resultsome solvent and plasticizer tend to be driven out of the polyvinylchloride plastisol and this results in a wavy and rough surface. Stillfurther problems associated with the use of such polyvinyl chlorideplastisol sealers and the like involve application technique. Sincepolyvinyl chloride plastisol sealers and the like must be applied inthicknesses of 20 mils of greater in order to obtain good adhesion, theycannot be feathered down to blend into other regions of the sheet metalwhich do not require the additional chip protection. Thus, the materialsmust be applied using a masking technique, whereby those regions whichare not to be coated with the sealer material are masked in a separateoperation prior to application of sealer. This masking is then removedafter the sealer is applied. It would obviously be desirable toeliminate these additional steps in the application of the chipresistant sealer material.

Accordingly, it is a preferred object of this invention to provide anovel solvent based, thermosetting coating composition adapted for useas a chip resistant primer, which primer may be applied in thicknessesof less than 20 mils and which may be feathered in such a manner as toblend with paint in other areas of the substrate which do no requirechip resistant coating.

It is a further object of the present invention to provide novel resinssuitable for use in solvent-based thermosetting coating compositions. Inthis regard, it is a particular object of the invention to providenovel, hydroxy functional epoxy-polyester graft copolymer resins whichare crosslinkable during cure, on the surface of a substrate.

It is another object of the invention to provide novel coatingcompositions which comprise crosslinkable hydroxy functionalepoxy-polyester graft copolymer and blocked polyisocyanate crosslinkingagent and which provide high crosslinking efficiency and tough, wellcured films at minimum bake temperatures, such as when applied asautomotive primers. In this regard, it is a particular object of theinvention to provide a novel hydroxy functional epoxy-polyester graftcopolymer resin/blocked polyisocyanate thermosetting coating compositionof sufficiently low Volatile Organic Content (VOC) to aid in meetinggovernmental emissions guidelines and yet which can be applied to asubstrate by spraying or other known method.

It is still another object of the invention to provide a compositionwhich will form a coating on a substrate, which coating has advantageousphysical properties including, for example, humidity and solventresistance, flexibility and corrosion protection for the underlyingsubstrate.

Additional aspects and advantages of the invention will be apparent fromthe following description thereof.

DISCLOSURE OF THE INVENTION

According to the present invention, novel crosslinkable hydroxyfunctional epoxy-polyester graft copolymer resins are provided which areadapted for use in thermosetting coating compositions, and which areespecially advantageous for use in high solids and chip resistant,organic solvent based thermosetting coating compositions. The hydroxyfunctional epoxy-polyester graft copolymer resins of the inventionpreferably have a number average molecular weight (M_(n)) of about 2,000to about 20,000 and are the reaction product obtained by polymerizationof lactone monomers in the presence of hydroxy functional epoxy amineadduct precursor. Such precursor preferably has a number averagemolecular weight (M_(n)) of between about 1,000 and about 4,000 and isthe reaction product of diepoxide chain extended with aliphatic diol andsubsequently chain terminated with hydroxy functional secondary amine.

Also according to the present invention, a novel, organic solvent based,thermosetting composition, in addition to solvent and any pigments andadditives such as, for example, catalyst, flow control agents and thelike, comprises the hydroxy functional epoxy-polyester graft copolymerresin of the invention and blocked polyisocyanate crosslinking agentincluding, but not limited to, blocked trifunctional isocyanurate ringcontaining polyisocyanates and oligoester modified blocked isocyanates.

Particularly preferred compositions of the invention are thoseformulated as high solids coating compositions having solids levels inthe range of 65-80% solids and suitable to be applied as chip resistantprimers in those areas of automotive panels, such as rocker panels,which are exposed to high levels of chipping. Such compositions may beapplied in thicknesses ranging from about 1 to 25 mils wet to obtainfinal coatings in the range of 1 to 12 mils dry, and may be feathereddown to blend in with paint applied to regions outside that requiringadditional chip resistant protection. Generally, the compositions ofthis solids level may be applied using hot spray equipment attemperatures in the range of from room temperature (i.e., 25° C.) toabout 160° F.

Other preferred compositions of the invention are those formulated ashigh solids coating compositions adapted to be applied by conventionalspraying onto a substrate. These high solids coating compositions mayhave a solids level in the range of 50-60% and are especially useful asa primer coating on the bare, unpolished metal surface of an automotivevehicle. As used herein, a high solids coating composition is one havinga volatile organic content of about 479 g/l (4.0 lb./gal.) or less.

Other features and advantages of this invention will become moreapparent from the following, detailed description thereof including thepreferred embodiments and best mode of carrying out this invention.

DETAILED DESCRIPTION OF THE INVENTION

The novel, hydroxy functional epoxy-polyester graft copolymer preferablyhas a number average molecular weight (M_(n)) of between about 2,000 andabout 20,000 and is formed by polymerization of lactone monomers in thepresence of hydroxy functional epoxy amine adduct precursor preferablyhaving a number average molecular weight (M_(n)) of between about 1,000and about 4,000. The hydroxy functional epoxy amine adduct precursor isthe reaction product of diepoxide chain extended with aliphatic diol andsubsequently chain terminated with hydroxy functional secondary amine.The polymerization of lactone monomers with the precursor is generallycarried out at a temperature between about 50° C. and about 300° C.,preferably at a temperature between about 130° C. and about 200° C., andthe polymerization reaction mixture comprises between about 10 and about80 weight percent hydroxy functional epoxy amine adduct precursor andbetween about 90 and about 20 weight percent lactone monomers.Preferably, the polymerization reaction mixture comprises between about35 and about 65 weight percent hydroxy functional epoxy amine adductprecursor and between about 65 and 35 weight percent lactone monomers.

Thermosetting compositions of the invention comprise the above hydroxyfunctional graft copolymer and blocked polyisocyanate crosslinking agentcomprising at least one isocyanate group which has been blocked byreaction with an active hydrogen bearing blocking agent. The blockedpolyisocyanate crosslinking agent is included in the composition in anamount such that upon deblocking of the blocked isocyanate groupsthereof at the cure temperature of the composition, the crosslinkingagent provides between about 0.5 and about 1.6 reactive isocyanategroups per reactive group on the hydroxy functional epoxy-polyestergraft copolymer.

Each of the above major components of the compositions as well as othercomponents and other aspects of the invention are described hereinafterin greater detail.

A. Hydroxy Functional Epoxy-Polyester Graft Copolymer

As described above, this copolymer is prepared by polymerizing lactonemonomer in the presence of a hydroxy functional epoxy amine adductprecursor which itself is the reaction product of diepoxide chainextended with aliphatic diol and subsequently chain terminated withhydroxy functional secondary amine.

It is believed to be a significant characterizing aspect of the hydroxyfunctional epoxy-polyester graft copolymer of the invention that thepolymerized lactone portion of the epoxy-polyester graft copolymer givesthe polymer flexibility as well as toughness, two key properties whenchoosing a primer for use in areas susceptible to chipping. It is afurther characterizing aspect of the copolymer that it includes epoxyresin portions, i.e. hydroxy terminated epoxy amine adduct precursor isused as an initiator to form the graft copolymer, which gives thecopolymer excellent corrosion resistance properties. Still further,because the graft copolymers of the invention are branched, they requirea minimum amount of crosslinking in order to obtain a suitable networkfor good coating integrity. Since crosslink bonds, e.g. isocyanate bondsas used in compositions of the invention, tend to be somewhat brittle,it is desirable to have a minimum number of such bonds. Still further,it is a characterizing aspect of the invention that the compositioncontains tertiary amine groups (i.e., since hydroxy functional secondaryamines are used to form the hydroxy functional epoxy ester resin,tertiary amine groups are present in the final resin). Tertiary aminegroups are excellent catalysts for the isocyanate crosslinking reactionused to cure compositions of this invention.

Preferred hydroxy functional epoxy-polyester graft copolymers of theinvention include significant aromatic content which is believed toenhance corrosion resistance properties. Even though aromatics tend toincrease the brittleness of polymers and compositions including suchpolymers, it is possible to include them since, as mentioned above, thepolymerized lactone portion of the hydroxy functional epoxy-polyestergraft copolymer gives the polymer increased flexibility which can morethan compensate for any such brittleness. A particularly preferredembodiment of the hydroxy functional epoxy-polyester graft copolymersresin of the invention is prepared from aromatic-containing diepoxide.

Each of the reactants employed in the preparation of the epoxy-polyestergraft copolymer is described in greater detail below.

(i) Diepoxide Reactant

The diepoxide reactant suitable for preparing the epoxy amine adductprecursor can be any of numerous diepoxides, including diphenol chainextended diepoxides, many of which are commercially available and whichwill be apparent to the skilled of the art in view of the presentdisclosure. While, ultimately, the choice of the epoxy reactant forpreparing the precursor resin will depend to an extent upon theparticular application intended for the coating composition, terminaldiepoxides, that is diepoxides bearing two terminal epoxide groups, aregenerally most preferred. These are generally more reactive andtherefore require reaction conditions under which undesirable sidereactions, for example, epoxy-epoxy reactions and gelation, can be moreeasily avoided.

Diepoxy resins, not previously extended with diphenol, may be used inthe preparation of the epoxy ester resin precursor. Preferred diepoxyresins of this type include Epon 828 (trademark) and Epon 829(trademark) which are nonextended diepoxides of the Epon (trademark)series (Shell Chemical Company, Houston, Tex.), as well ascycloaliphatic diepoxy resins such as; the Eponex (trademark) series(Shell Chemical Company); hydantoin epoxy resins such as, for example,Resin XB2793 (trademark; Ciba-Geigy Corporation, Ardsley, N.Y.); and anyof a wide variety of acyclic or cyclic aliphatic diepoxides such as, forexample, 1,4-butanediol diglycidyl ether and 4-vinylcyclohexene dioxideand the like. Other suitable diepoxides are available and will beapparent to the skilled of the art in view of the present disclosure.

Still further, diepoxides previously extended with diphenol may beemployed in forming the precursor and numerous such extended diepoxidesare known and are commercially available. These include certain of thewell known bisphenol-A epichlorohydrin epoxy resins of the Epon(trademark) series (Shell Chemical Company), e.g., Epon 1001 and Epon1004, and the DER (trademark) series (Dow Chemical Company, Midland,Mich.), e.g., DER 332. These diglycidyl ether bisphenol-A resins orhigher molecular weight analogs thereof, are preferred in view of theircost and commercial availability. Any of the commercially availablediphenol extended epoxy resins such as those discussed above may befurther extended, if desired, by diphenol in order to give highermolecular weight materials having desirable properties. Also, it will beunderstood from the foregoing that any mixture of compatible diepoxidesmay be used.

In addition to the diepoxide, a portion of the epoxy functionality canbe provided by any compatible monoepoxy compound or polyepoxy compoundor mixture of such compounds. The polyepoxide can be any of the wellknown types such as polyglycidyl ethers of polyphenols. These can beproduced by etherification of polyphenol and epihalohydrin in thepresence of alkali. It will be recognized by the skilled of the art inview of the present disclosure, that in some instances, particularlywhere a coating composition of high solids content is less important, itmay be desirable to incorporate polyepoxide of higher molecular weight.Preferably, any such polyepoxide contains free hydroxyl groups inaddition to epoxide groups.

While polyglcydiyl ethers of polyphenol can be employed, it may bedesirable to react a portion of the reactive sites (hydroxyl or in someinstances epoxy) with a modifying material to vary the filmcharacteristics of the resin. The epoxy resin may be modified, forexample, with isocyanate group containing organic materials or otherreactive organic materials.

Other useful polyepoxides are the novolak resins including, for example,the novolak epoxy resins ECN 1235 (trademark) and ECN 1273 (trademark),Ciba-Geigy Corporation.

According to preferred embodiments of the present invention, epoxidecompounds other than diepoxide compounds provide no more than about 15%and most preferably substantially none of the total epoxidefunctionality in the reactants used to form the epoxy amine adductresin.

(ii) Aliphatic Diol Reactant

The aliphatic diol reactants suitable for reaction with the diepoxidereactant in chain extension reaction include numerous commerciallyavailable materials, many of which will be readily apparent to theskilled of the art in view of the present disclosure. Preferredaliphatic diols have the general formula OH--R--OH, where R is adivalent, aliphatic linking moiety substantially unreactive with thediepoxide resin, for example, (CH₂)_(n) wherein n is preferably from 1to about 8, and the like. Both saturated and unsaturated aliphatic diolsare suitable. Inorganic moieties, for example sulfonyl and the like,also are suitable. Diols of this character provide good reactivity withdiepoxides described above and provide, ultimately, cured coatings ofthe invention having excellent physical properties, most notablyexcellent corrosion protection. It will be apparent to the skilled ofthe art in view of the present disclosure that R should be substantiallyunreactive with the diepoxide and the acid component employed inpreparation of the hydroxy functional epoxy ester precursor.

Preferably the diol has a number average molecular weight (M_(n))between about 60 and about 500, more preferably between about 60 andabout 200. Particularly preferred diols include those according toformula (I) above, wherein R is selected from the group consisting of astraight or branched alkylene or alkylidene moiety of one to about 10carbons, preferably having three to four carbons. Most preferred areterminal diols, that is, diols bearing two terminal hydroxyfunctionality, for example, 1,6-hexanediol, since these generally aremore reactive. Other suitable aliphatic diols include primary/secondaryand secondary/secondary carbon hydroxy substituted diols. Diols bearingtertiary hydroxyl groups are least preferred due to their lowerreactivity. Thus, preferred diols include, for example, alkylsubstituted or unsubstituted propanediol, butanediol, pentanediol,hexanediol, and a mixture of any of them. Preferred aliphatic diolsinclude, aliphatic diols of about 2 to 20 carbons, for example, ethyleneglycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol,3-ethyl-1,3-hexanediol and the like, or a compatible mixture of any ofthem. Other suitable aliphatic diols for forming the epoxy ester resinprecursor of the present invention will be apparent to the skilled ofthe art in view of the present disclosure.

Preferably, the chain extended diepoxide to be chain terminated with thehydroxy functional secondary amine has a number average molecular weight(M_(n)) between about 1,200 and about 3,500, and more preferably betweenabout 1,600 and about 2,400.

(iii) Hydroxy Functional Secondary Amine Reactant

The hydroxy functional secondary amine which is reacted in chainterminating reaction with the reaction product of the above describeddiepoxide and aliphatic diol may be selected from a broad class ofaliphatic, cycloaliphatic and aromatic hydroxy functional amines.

Numerous such amines, which may bear mono- or dihydroxy functionalitywill be apparent to those skilled in the art in view of the presentdisclosure. Exemplary of such amines are those having the formula:##STR1## wherein R' and R" are selected from the group consisting ofaliphatic, cycloaliphatic and aromatic radicals which will not interferewith the chain termination reaction between the chain extended diepoxideand the hydroxy functional secondary amine. R' and R" in the aboveformula may be the same or different, but preferably should be of thesame nature. X may be selected from hydrogen and hydroxyl radical. Whilethe hydroxyl group on R' and/or R" may be other than primary, primaryhydroxyls are preferred since such primary hydroxyl groups are morereactive.

Examples of preferred radicals R and R' for the hydroxy functional amineof the above formula are:

    ______________________________________                                        (CH.sub.2).sub.n      where n = 1-5;                                          (CH.sub.2 CH.sub.2 O).sub.n CH.sub.2 CH.sub.2                                                       where n = 1-12;                                          ##STR2##             where n = 1-12; and                                      ##STR3##             where n = 1-12                                          ______________________________________                                    

Preferably R' and R" are methylene, ethylene, or lower alkylene groupsbut they may be any other noninterfering radical including those, forexample, such as benzyl, oxyalkylene, etc. Particularly preferredprimary hydroxy bearing amines for use in preparing the hydroxyfunctional epoxy amine adduct are diethanol amine, methylethanol amine,dipropanol amine and methylpropanol amine.

The hydroxy functional epoxy amine adduct precursor used to initiatelactone polymerization in the preparation of the epoxy-polyester graftcopolymer of the invention can be made according to techniques wellknown to the skilled of the art. The chain extension, where necessary,and chain termination reactions are carried out sequentially, with thechain extension of the diepoxide being carried out first. Accordingly,diepoxide and aliphatic diol are charged into a suitable reactor andheated. The reactants are used in relative proportions to yield a chainextension reaction product bearing two unreacted epoxy groups andpreferably substantially no unreacted diol. Suitable separationtechniques are known to the skilled of the art for removal of unusedreactants. It should be recognized that to assure rapid and/or morecomplete reaction of the diepoxide with the diol, it is usuallypreferred to have a catalyst present. The use of catalyst has been foundto be advantageous in the preparation of the epoxy ester resin. Epon 829(trademark), mentioned above, as sold, provides a proprietary catalyst.Epon 828 (trademark), is substantially the same but does not providesuch catalyst. Suitable catalysts are commercially available and includeany of the well known catalysts for epoxy-hydroxy reactions such as, forexample, sodium carbonate, lithium neodecanoate and other organometallic catalysts and tertiary amines, such as benzyl dimethylamine,which is preferred. Still other preferred catalyst includeformylmethylene triphenylphorane, formylmethyltriphenylphosphoniumchloride, methyltriphenylphosphonium iodide, and ethyltriphenylphosphonium acetate. Other suitable catalysts will be apparent to thoseskilled in the art in view of the present disclosure.

The reaction mixture is heated to at least about 135° C. (280° F.) atwhich point, in the presence of catalyst, exothermic reaction willproceed with or without further heating. Typically, the reaction mixturewill then reach about 170° C.-190° C. (340° F.-370° F.), depending uponthe batch size and reactor vessel insulation, etc. In the absence ofcatalyst, such exotherm is typically not observed and continued heatingis required. The progress of the reaction can be followed by measuringweight per epoxy (WPE), i.e., epoxy equivalent weight.

After completion of the chain extension reaction of diepoxide with diol,the diepoxide reaction product is reacted with the hydroxy functionalsecondary amine reactant in chain terminating reaction in approximately1 to 1 equivalent ratio. This ratio is preferred since excess epoxycould result in gelation of the reaction mixture, while excess aminereactant remaining in the reaction mixture could compete with the epoxyester resin precursor for lactone monomers during formation of theepoxy-polyester graft copolymer. For this reason, if excess aminereactant is used during formation of the precursor, it should preferablybe removed prior to reaction of the precursor with the lactone monomers.

(iv) Lactone Monomers

The lactone reactant may be any lactone, or combination of lactones,having at least six carbon atoms, for example, from six to eight carbonatoms, in the ring and at least one hydrogen substituent on the carbonatom which is attached to the oxy group in said ring. In one aspect, thelactone used as a reactant can be represented by the general formula:##STR4## in which n is at least four, for example, from four to six, atleast n+2 R's are hydrogen, and the remaining R's are substituentsselected from the group consisting of hydrogen, alkyl, cycloalkyl,alkoxy and single ring aromatic hydrocarbon radicals. Lactones havinggreater numbers of substituents other than hydrogen on the ring, andlactones having five or less carbon atoms in the ring, are consideredunsuitable for the purposes of the invention because of the tendencythat polymers thereof have to revert to the monomer, particularly atelevated temperature.

The lactones preferred in this invention are the epsilon-caprolactoneshaving the general formula: ##STR5## wherein at least six of the R's arehydrogen and the remainder are hydrogen, alkyl, cycloalkyl, alkoxy orsingle ring aromatic hydrocarbon radicals, none of the substituentscontain more than about twelve carbon atoms, and the total number ofcarbon atoms in the substituents on a lactone ring does not exceed abouttwelve. Unsubstituted epsilon-caprolactone, in which all the R's arehydrogen, is derived from 6-hydroxyhexanoic acid and is most preferred.Substituted epsilon-caprolactones, and mixtures thereof, are availableby reacting a corresponding substituted cyclohexanone with an oxidizingagent such as peracetic acid.

Among the substituted epsilon-caprolactones considered most suitable forthe purposes of the invention are the various monoalkylepsilon-caprolactones such as the monomethyl-, monoethyl-, monopropyl-,monoisopropyl-, etc. to monododecyl epsilon-caprolactones; dialkylepsilon-caprolactones in which the two alkyl groups are substituted onthe same or different carbon atoms, but not both on the epsilon carbonatom; trialkyl epsilon-caprolactones in which two or three carbon atomsin the lactone ring are substituted, so long as the epsilon carbon atomis not disubstituted; alkoxy epsilon-caprolactones such as methoxy andethoxy epsilon-caprolactones; and cycloalkyl, aryl, and aralkylepsilon-caprolactones such as cyclohexyl, phenyl and benzylepsilon-caprolactones.

Lactones having more than six carbon atoms in the ring, e.g.,zeta-enatholactone and eta-caprylolactone may also be polymerized inaccordance with the invention.

Polymerization of the lactones in accordance with this invention iscarried out in conventional manner. While not wishing to be bound bytheory, it currently is understood that the polymerization is initiatedby reaction with a compound having at least one reactive hydrogen, withor without the aid of a catalyst, by opening the lactone ring and addingit as an open chain without forming water of condensation--in this casethe initiator compound being the hydroxy functional epoxy amine adductprecursor described above. The polymerization reaction mixture comprisesbetween about 10 and about 80 weight percent of the above-describedhydroxy functional epoxy ester resin and between about 10 and about 20weight percent of the lactone monomers. Preferably, the polymerizationreaction mixture comprises between about 35 and about 65 weight percentof the hydroxy functional epoxy amine adduct and between about 65 andabout 35 weight percent of the lactone monomers.

To initiate and continue the polymerization of the lactone, the lactoneand the initiator (i.e., the precursor) are preferably heated to atemperature between about 130° and 200° C. to achieve a practical anddesirable rate of reaction with a minimum of decomposition. Thetemperature may be considerably lower however, i.e., as low as about 50°C. at the sacrifice of speed of reaction. It may also be considerablyhigher, i.e., up to about 300° C., although care must be taken at suchhigher temperatures because of the more likely losses, at temperaturesabove 250° C., due to decomposition or undesirable side reactions.Generally, therefore, a temperature range of 50° to 300° C. isconsidered operable and a more limited range between about 130° and 200°C. is considered preferable.

The polymerization may be, and preferably is, carried out with the useof a catalyst, such as a basic or neutral ester interchange catalyst, toaccelerate the reaction. Among catalysts suitable for this purpose aresuch metals as lithium, sodium, potassium, rubidium, cesium, magnesium,calcium, barium, strontium, zinc, aluminum, titanium, cobalt, germanium,tin, lead, antimony, arsenic and cerium, as well as the alkoxidesthereof. Additional suitable catalysts are, by way of example, thecarbonates of alkali- and alkaline earth metals, zinc borate, leadborate, zinc oxide, lead silicate, lead arsenate, litharge, leadcarbonate, antimony trioxide, germanium dioxide, cerium trioxide,cobaltous acetate and aluminum isopropoxide. Catalyst concentrationsbetween about 0.001 and 0.5%, based on the weight of the startinglactones, are suitable. The preferred range is from 0.01 to 0.2%.

The hydroxy functional epoxy-polyester graft copolymerization productsobtained in accordance with the invention have molecular weightsgenerally upwards of about 2,000 and preferably within the range ofabout 4,000 to about 20,000, although molecular weights below andsubstantially above this range are obtainable if desired. While notwishing to be bound by theory, it presently is understood that thehydroxy functional epoxy-polyester graft copolymer has reactive terminalhydroxyl groups, the number of reactive terminal groups depending uponthe functionality of the initiator. Further, it presently is understoodthat they are characterized by the presence of series of interconnected,substantially linear units or groups composed of carbon, hydrogen andoxygen. The interconnected units are opened lactone residues such havinga terminal oxy group at one end, a carbonyl group at the other end, anintermediate chain of at least five carbon atoms and at least onehydrogen substituent on the carbon atom in the intermediate chain thatis attached to the terminal oxy group. The oxy group of one lactoneresidue is connected to the carbonyl group of an adjacent lactoneresidue in the series and the oxy group of the last lactone residue in aseries is connected to a hydrogen to form a terminal hydroxyl group atone end of the series.

B. Crosslinking Agent

The crosslinking agent employed in the novel solvent based coatingcompositions of the invention comprises blocked polyisocyanate. Thenovel solvent based coating compositions of the invention, as a resultof employing blocked polyisocyanate crosslinking agents, exhibitexceptional shelf stability even when corrosion inhibiting pigments suchas zinc chromate are used in high concentrations.

As used herein "blocked polyisocyanate" means an isocyanate compoundcontaining two or more isocyanato groups, all of which have been reactedwith a material which will prevent reaction of the isocyanate group atroom temperature with compounds that conventionally react with suchgroups, and at least some of which will permit that reaction to occur athigher (cure) temperatures. In general the blocked polyisocyanate may beprepared by reacting a sufficient quantity of an active hydrogencontaining blocking agent with the polyisocyanate to insure that no freeisocyanato groups are present. The blocking agent may be represented bythe formula BH and may be selected from numerous materials, hereinafterdiscussed, which bear an active hydrogen.

The blocked polyisocyanate crosslinking agent is included incompositions of the invention in amounts such that upon deblocking ofthe blocked isocyanato groups at the cure temperature of thecomposition, the crosslinking agent will provide between about 0.5 andabout 1.6, preferably between about 0.8 and about 1.3, reactiveisocyanato groups per reactive group on the film forming graft copolymerof the coating composition as described above. Blocked polyisocyanatesof numerous types may be employed in the compositions of the invention.Particularly suitable blocked polyisocyanates, which will be discussedfurther hereinafter, include blocked polymethylene polyphenolisocyanates, isocyanurate ring containing blocked polyisocyanates andcertain oligoester modified blocked polyisocyanates.

In the preparation of the blocked polyisocyanate crosslinking agent, anysuitable organic polyisocyanate may be used. Representative examples arethe aliphatic compounds such as trimethylene, tetramethylene,pentamethylene, hexamethylene, 1,2-propylene, 1,2-butylene,2,3-butylene, 1,3-butylene, ethylidene and butylidene diisocyanates; thecycloalkylene compounds such as 1,3-cyclopentane, 1,4-cyclohexane, and1,2-cyclohexane diisocyanates; the aromatic compounds such asm-phenylene, p-phenylene, 4,4'-diphenyl, 1,5-naphthalene, and1,4-naphthalene diisocyanates, the aliphatic-aromatic compounds such as4,4'-diphenylene methane, 2,4- or 2,6-tolylene, or mixtures thereof,4,4'-toluidine, and 1,4-xylylene diisocyanates; substituted aromaticcompounds such as dianisidine diisocyanate, 4,4'-diphenyletherdiisocyanate and chlorodiphenylene diisocyanate; the triisocyanates suchas triphenyl methane-4,4'4"-triisocyanate, 1,3,5-triisocyanate benzeneand 2,4,6-triisocyanate toluene; the tetraisocyanates such as4,4'-diphenyl-dimethyl methane-2,2',5,5'-tetraisocyanate; and thepolymerized polyisocyanates such as tolylene diisocyanate dimers andtrimers, and the like.

In addition, the organic polyisocyanate may be a prepolymer derived froma polyol including polyether polyol or polyester polyol, includingpolyethers which are reacted with excess polyisocyanates to formisocyanate-terminated prepolymers. The polyols may be simple polyolssuch as glycols, e.g., ethylene glycol and propylene glycol, as well asother polyols such as glycerol; trimethylolpropane, pentaerythritol, andthe like, as well as mono-ethers such as diethylene glycol, tripropyleneglycol and the like and polyethers, i.e., alkylene oxide condensates ofthe above. Among the alkylene oxides that may be condensed with thesepolyols to form polyethers are ethylene oxide, propylene oxide, butyleneoxide, styrene oxide and the like. These are generally calledhydroxyl-terminated polyethers and can be linear or branched. Examplesof polyethers include polyoxyethylene glycol, polyoxypropylene glycol,polyoxytetramethylene glycol, polyoxyhexamethylene glycol,polyoxynonamethylene glycol, polyoxydecamethylene glycol,polyoxydodecamethylene glycol and mixtures thereof. Other types ofpolyoxyalkylene glycol ethers can be used. Especially useful polyetherpolyols are those derived from reacting polyols such as ethylene glycol,diethylene glycol, triethylene glycol, 1,4-butylene glycol, 1,3-butyleneglycol, 1,6-hexanediol, and their mixtures; glycerol, trimethylolethane,trimethylolpropane, 1,2,6-hexanetriol, pentaerythritol,dipentaerythritol, tripentaerythritol, polypentaerythritol, sorbitol,methyl glucosides, sucrose and the like with alkylene oxides such asethylene oxide, propylene oxide, their mixtures, and the like.

A particular class of aromatic polyisocyanates which may be employed inthe novel solvent based coating compositions of the invention arepolymethylene polyphenol isocyanates having the formula: ##STR6##wherein n equal 1 to 3. Such compounds, sold under the tradename "PAPI"by the UpJohn Chemical Company of Kalamazoo, Mich., have proven to beparticularly useful in compositions of the invention, resulting incompositions exhibiting desirable toughness in the final cured coating.

The active hydrogen containing blocking agents which are reacted withthe above described organic diisocyanates may be selected from numerousblocking agents which will be apparent to those skilled in this art.Representative of those blocking agents which are preferred are thoseselected from the group consisting of (i) aliphatic, cycloaliphatic andaromatic alkyl monoalcohols; (ii) hydroxyl amines; (ii) oximes; (iv)lactams; and (v) triazoles. Any suitable aliphatic, cycloaliphatic oraromatic alkyl monoalcohol may be used as a blocking agent in accordancewith the present invention. For example, aliphatic alcohols, such asmethyl, ethyl, chloroethyl, propyl, butyl, amyl, hexyl, heptyl, octyl,nonyl, 3,3,5-trimethylhexyl, decyl, and lauryl alcohols, and the likemay be employed. Suitable cycloaliphatic alcohols include, for example,cyclopentanol, cyclohexanol and the like, while aromatic-alkyl alcoholsinclude phenylcarbinol, methylphenylcarbinol, and the like. Minoramounts of even higher molecular weight relatively non-volatilemonoalcohols may be used, if desired, to serve as plasticizers in thecoatings provided by the invention. Examples of hydroxyl amines whichmay be employed as blocking agents include ethanol amine and propanolamine. Suitable oxime blocking agents include, for example,methylethylketone oxime, acetone oxime and cyclohexanone oxime. Examplesof lactams which may be used as blocking agents are caprolactam,butyrolactam and pyrrolidone, while suitable triazoles include compoundssuch as 1,2,4-triazole, 1,2,3-benzotriazole, 1,2,3-tolyltriazole and4,5-diphenyl-1,2,3-triazole. Particularly preferred active hydrogencontaining blocking agents are methylethyl ketoxime and 2-ethylhexanol.

(i) Isocyanurate Ring Containing Blocked Isocyanate Compounds

Within the scope of the above general class of blocked polyisocyanatecrosslinking agents, a particular class type of blocked polyisocyanatecrosslinking agent which may be employed in the novel solvent basedcoating compositions of the invention comprises isocyanurate ringcontaining blocked isocyanate compounds. In general, these blockedpolyisocyanates may be formed by blocking with the aforementionedblocking agent isocyanurate ring containing polyisocyanates. Thesecompounds may be formed by cyclotrimerization of difunctionalisocyanates. Usually, the reaction does not stop in this stage andcontinues through the formation of polyfunctional oligomers or a mixtureof such oligomers with a portion of the pure trifunctionalpolyisocyanate. Mixtures of trifunctional product and variouspolyfunctional oligomers are commercially available.

A particularly desirable blocked polyisocyanate crosslinking agent isthe blocked form of the pure trifunctional isocyanurate represented bythe following formula: ##STR7## wherein R is selected from the groupconsisting of aliphatic, cycloaliphatic and aromatic groups andcombinations thereof and B is the residue of an active hydrogencontaining blocking agent. More specifically, this compound is disclosedin U.S. Pat. No. 4,491,663, the disclosure of which is herebyincorporated by reference.

(ii) Oligoester Modified Blocked Polyisocyanates

Still further particular blocked polyisocyanates useful as crosslinkingagents in the novel solvent based coating compositions of this inventionare oligoester modified blocked polyisocyanates prepared from aparticular class of oligoester diols and triols. A first type of sucholigoester modified blocked polyisocyanates is prepared from organicdiisocyanates bearing one isocyanato group more reactive than the other,with the more reactive isocyanato first being blocked with a blockingagent and the remaining isocyanato group then being reacted withhydroxyl functionality of an oligoester diol or triol as referred toabove. The second type of oligoester modified blocked polyisocyanate maybe prepared by reacting oligoester diols from the aforementioned classof oligoesters with an excess of organic diisocyanate so as to form anisocyanato terminated prepolymer followed by blocking of the terminalisocyanato groups of the prepolymer with an active hydrogen containingblocking agent. Each of these materials is particularly useful in thecompositions of the invention and produces final cured coatingcompositions exhibiting outstanding flexibility.

Oligoesters of the type employed in the preparation of thesecrosslinking agents are described in U.S. Pat. No. 4,322,508 issued Mar.30, 1982, the disclosure of which is hereby incorporated by reference.The hydroxy functional oligoesters within the useful class of materials(i) have a number average molecular weight (M_(n)) of between about 150and about 3000, preferably between about 230 and about 1000, (ii) bear 2or 3 hydroxyl groups per molecule, and (iii) are formed by anesterification reaction between a carboxylic acid and an epoxide. Theesterification reaction products are selected from the group consistingof:

(a) the esterification reaction product of polycarboxylic acid, i.e.,carboxylic acid bearing 2 or more carboxyl groups, and monoepoxide;

(b) the esterification reaction product of polyepoxide, i.e., a compoundhaving 2 or more epoxide groups, and monocarboxylic acid, preferablycontaining no ethylenic unsaturation, and bearing no hydroxyfunctionality;

(c) the esterification reaction product of hydroxy functional carboxylicacid and mono- or polyepoxide, preferably monoepoxide;

(d) the esterification reaction product of monocarboxylic acid andhydroxy functional mono- or polyepoxide, preferably monoepoxide; and

(e) mixtures of (a)-(d).

As noted above, the first type of oligoester modified blockedpolyisocyanate crosslinking agent is prepared by (i) reacting organicdiisocyanate bearing one isocyanato group which is more reactive thanthe other with a sufficient amount of an active hydrogen containingblocking agent to react substantially with all of the more reactiveisocyanate groups, thus providing a half-blocked diisocyanate and (ii)reacting this half-blocked intermediate with the above discussedoligoester. The organic diisocyanates employed in this synthesis, aswell as the active hydrogen containing blocking agents, are discussedabove in connection with the preparation of the isocyanurate ringcontaining blocked isocyanate crosslinking agents useful in compositionsof the invention. The organic polyisocyanate-blocking agent adductintermediate is formed by reacting a sufficient quantity of the blockingagent with the organic diisocyanate to insure that one of the two --NCOgroups on the diisocyanate is reacted. The reaction between the organicdiisocyanate and the blocking agent is exothermic; therefore, thediisocyanate and the blocking agent are preferably admixed attemperatures no higher than about 80° C., preferably below about 50° C.,to minimize the exothermic effect.

This intermediate is next reacted with the oligoester diol or trioldescribed above so as to react substantially all free or unblockedisocyanato groups of the diisocyanate/blocking agent intermediate withhydroxyl groups of the oligoester. This reaction is carried outdesirably at a temperature of about 80°-120° C.

As also discussed above, the second type of oligoester modified blockedpolyisocyanate crosslinking agent useful in the novel solvent basedcoating compositions of the invention is prepared by reacting an excessof organic diisocyanate with an oligoester diol from the above describedclass of oligoesters followed by reaction of the terminal isocyanatogroups formed on the resultant prepolymer with an active hydrogencontaining blocking agent as described above so as to react withsubstantially all the isocyanato groups. The diisocyanate startingmaterial is used in excess in amounts sufficient to insure that theintermediate is isocyanate terminated. Therefore, it is preferable thatthe organic diisocyanates and the dihydroxy functional oligoester bereacted in a molar ratio of from greater than 1:1 up to 2:1. Numerousdiisocyanates of the type described hereinbefore may be employed in thepreparation of this intermediate. While it is not necessary that oneisocyanato group be more reactive than the other, the preparation ofthis type of crosslinking agent does not preclude the use of suchmaterial.

C. General Discussion--Other Aspects of Invention and Other Components

The coating compositions of the invention have been found to provide acured coating having the advantageous physical properties describedabove, over a wide range of cure temperatures and a wide range of solidslevels. More specifically, the coating compositions according topreferred embodiments of the invention have been found to cure attemperatures from as low as about 120° C. or less within about 15minutes or less, and yet to cure and suffer no significant loss ofadvantageous physical properties at temperatures as high as about 200°C. or more for periods up to about 60 minutes or more. Consideredtogether with the storage stability of the coating composition, it canbe readily recognized that the present invention provides a highlysignificant advance in the coating composition art.

It will be within the skill of the art to determine the proper volatileorganic content for a given composition of the invention and for a givenapplication. For compositions to be used as spray-applied coatingcompositions, preferred solvents have relatively low volatility attemperatures appreciably below their boiling points such that solventevaporation is low during storage and/or application of the coatingcomposition to the substrate. A suitable solvent system may include, forexample, toluene, methyl ethyl ketone, isobutyl acetate, xylene,cellosolve acetate, acetone and a mixture of any of them. Other solventswhich may be employed include terpenes, aliphatic and aromatic naphthas,and the like. Additional suitable solvents are commercially availableand will be apparent to the skilled of the art in view of the presentdisclosure.

Any solvent allowed to remain in the cured coating should be inert so asto avoid adverse effect upon the cured coating or upon another coatinglayer used in conjunction with it during the curing process orthereafter. Preferrably, the cured coating is substantially free ofsolvent.

Sufficient solvent is used to reduce the viscosity of the coatingcomposition to a level suitable for application to the substrate in thedesired manner. In those cases where the composition is to be applied asa chip resistant primer, the amount of solvent will be reduced so as togive a solids level of about 65-80%. Such higher solids materials aregenerally applied using hot spray equipment.

Flow control agent(s), for example, polybutyl acrylate; wettingagent(s), for example, silicone; pigments; pigment dispersants;corrosion inhibitors, for example, chromate pigments, numerous of all ofwhich are known to the skilled of the art, may be employed in thecoating compositions of the invention. In addition, suitable reactiveadditives can be used, including, for example, low molecular weight diolflow control agents and reactive diluents.

Compositions of the invention, and in particular the chip resistantprimers of the invention, may also include anti-settling or anti-saggingagents to control the thixotropic properties of the composition.Exemplary of available materials suitable for this purpose are Dislon(trademark) 6900-20X manufactured by Kusumoto Chemicals, Ltd., Tokyo,Japan and solid by King Industries, Norwalk, CT 06852; Bentone(trademark) 38, N. L. Industries, Highstown, N. J. 08520; and Cab-O-Sil(trademark) M-5, Cabot Corporation.

Curing the coating composition requires baking for sufficient time atsufficiently elevated temperature to react the crosslinking agent withthe hydroxyl functionality of the hydroxy functional epoxy-polyestergraft copolymer. The time and temperature required to cure the coatingare interrelated and depend upon the particular hydroxy functionalityepoxy-polyester graft copolymer resin, crosslinking agent, solvent andother materials, if any, and the amount of each comprising the coatingcomposition. The coating compositions according to preferred embodimentsof the invention, as described above, have been found to provide thebest coating results when cured at about 150° C. (300° F.) for 20minutes. It is a highly significant advantage of the invention, however,that these same coating compositions can withstand, for example,temperatures as high as about 200° C. (390° F.) for periods of time aslong as about 60 minutes. Accordingly, great flexibility is provided inboth designing and implementing a curing schedule for parts coated withthe coating compositions of the invention. Thus, in the assembly ofautomotive vehicles, for example, vehicles unavoidably held in a curingoven for long periods of time during unplanned assembly line shut-downsare recovered with cured and unharmed coatings.

High solids coating compositions according to the present invention,comprising the novel crosslinkable hydroxy functional epoxy-polyestergraft copolymer resins of the invention, especially the preferred resinsdescribed above and blocked polyisocyanate crosslinking agent,especially the preferred materials described above, have been found toafford cured coatings with improved corrosion resistance and chipresistance, thus representing a highly advantageous advance in the art.

A most preferred use of the coating composition of the invention is ashigh solids hot sprayable chip resistant primer for use on a bare metalsubstrate such as for an automotive vehicle body which is subject tochipping. Primer compositions typically are pigmented and any pigmentscommonly included in primer compositions for metal substrates andacrylic dispersion topcoats such as, for example, carbon black, ironoxide, lithopone, magnesium, silicate, silica, barium sulfate, TiO₂,chrome yellow, calcium chromate, strontium chromate, zinc potassiumchromate any the like may be used. The primer can be pigmented accordingto known methods including, for example, by grinding pigments in aportion of the curable resin and adding to the primer composition.

The pigment-to-binder ratio of the chip resistant primer may be fromabout 0.5/1 to about 2/1 by weight, respectively. It is preferred,however, to use a primer having a pigment-to-binder ratio of from about1:1 to about 1.5:1 by weight, respectively.

In preferred embodiments of this invention pigments and thixotropicagents desirably are dispersed with epoxy ester resins which do not havean elastomeric component as does the hydroxy functional epoxy-polyestergraft copolymer employed as the primary film forming resin of thecomposition of this invention. It has been found that, in addition tobeing very effective dispersing agents for the preparation of pigmentmillbases and thioxtropic dispersions, non-elastomeric epoxies give thecompositions toughness. One type of epoxy useful for this purposecomprises the reaction product of diepoxide, dimer acid and a mixture ofsoya fatty acid and propionic acid (see Example 1). Other epoxy esterresins useful for this purpose are those disclosed in U.S. patentapplication Ser. Nos. 448,886 filed June 14, 1982 (abandoned), and431,465 filed Sept. 30, 1982 (abandoned), and in U.S. Pat. No.4,491,641, all assigned to the assignee of this application. Theseresins comprise the simultaneous reaction product of diepoxide with (i)diphenol, dicarboxylic acid or a mixture of them in chain extensionreaction and (ii) fatty acid in chain terminating esterificationreaction. Still other suitable epoxy resins useful for dispersingpigment and thixotropic agents will be apparent to the skilled of theart in view of the present disclosure.

No special expedients are necessary in formulating the primercompositions of this invention. For example, they may be prepared simplyby incorporating the resinous components in a suitable solvent system.Thus, for example, by suitable mixing or agitation, each resinouscomponent may be dissolved in a solvent and the resulting solutionscombined to form finished primer compositions.

The solvent system may be any suitable combination of organic solventsas described above. For a high solids, hot sprayable, automotive vehiclechip resistant primer, the solvent will comprise preferably about 20 toabout 40 percent by weight of the total coating compositions, althoughof course, larger or smaller amounts may be utilized depending upon thesolids content desired.

The primer is generally maintained at about 65 to about 80 percentsolids content for hot spraying purposes with conventional thinners suchas aromatic hydrocarbons, commercial petroleum cuts which areessentially aromatic, and the like, and sprayed onto the metal base orother substrate and cured. The primer may be applied in greaterthickness of 1 to 25 mils wet, preferably 10 to 25 mils wet, in order toobtain final coatings in the desired range of 5-11 mils dry in regionshighly susceptible to chipping and is then feathered down in thicknessto the thickness of paints in areas not receiving a chip resistantprimer. The primer is cured at elevated temperatures by any convenientmeans such as baking ovens or banks of infra-red heat lamps. Curingtemperatures are preferably from about 135° C. to about 165° C.,although curing temperatures from about 100° C. to about 230° C. may beemployed, if desired.

The invention will be further understood by referring to the followingdetailed examples. It should be understood that these specific examplesare presented by way of illustration and not by way of limitation.Unless otherwise specified, all references to "parts" are intended tomean parts by weight.

EXAMPLE 1 Preparation of Epoxy-Ester Dispersing Resin

An epoxy-ester dispersing resin was prepared according to the followingprocedure. Into a suitable reactor were charged 1280 parts Epon 829(trademark; Shell Chemical Company; diepoxide resin), 954 parts Empol1016 (trademark; Emery Industries, Inc.; dimer acid), 364 parts soyafatty acid, 268 parts 2,2-bis(hydroxymethyl)propionic acid, and 13 partslithium neodeconoate. The temperature of the mixture was brought up toabout 180° C., at which point an exothermic reaction took place thatraised the temperature to about 200° C. After about one hour the acidnumber was found to be less than 2. 940 parts Solvesso 100 and 305 partsSolvesso 150 were added and the mixture was cooled. The resin was foundto have a viscosity of Z₇ at 70.0% non-volatiles.

EXAMPLE 2

In this Example an aliphatic diol is prepared for use in making hydroxyfunctional epoxy amine adduct precursor. In a suitable reactor arecharged 1875 parts azelaic acid and 4 parts of an organo-chromium(III)catalyst sold under the trade designation AMC-2 by Cordova ChemicalCompany, Sacramento, Calif. The mixture is slowly heated to 65° C.without agitation to melt the azelaic acid. The agitator is turned onand 1200 parts propylene oxide are added dropwise over 6 hours tomaintain the mixture at 65°-70° C. Subsequently, about 30 minutes afterthe addition of propylene oxide is completed, the acid number isdetermined to be less than 1. A partial vacuum was applied to remove anyexcess propylene oxide; the mixture is then allowed to cool. Theresulting product has a viscosity of L at 100% solids.

EXAMPLE 3

In this Example is prepared a hydroxy functional epoxy-polyester graftcopolymer according to the invention. In a suitable reactor are charged640 parts Epon 829 (trademark: Shell Chemical Company; piepoxide resin),151 parts bisphenol A, and 122 parts aliphatic diol prepared accordingto Example 2. The temperature of the mixture is slowly raised to 170°C., at which point an exothermic reaction occurs which raises thetemperature to 180°-190° C. The mixture is maintained at 175° C. for 1hour, and then cooled to 120° C. Then 3 parts benzyl dimethyl amine areadded to the mixture and the progress of the reaction is followed byepoxy equivalent weight ("WPE") measurement; after two hours the WPE isdetermined to be 850-950. 116 parts diethanolamine and 230 partsSolvesso 150 (trademark; Shell Chemical Company; aromatic solvent) areadded to the mixture. The temperature of the mixture is raised to 130°C., at which point a mild exotherm occurs which raises the temperatureto about 160° C. The mixture is maintained at that temperature for 1hour. Then 1029 parts epsilon-caprolactone and 1 part dibutyl tin oxideare added to the mixture. The mixture is heated to 130° C. and a mildexotherm occurs that raises the temperature to about 170° C. The mixtureis maintained at 170° C. for 2 hours; the % solids of the mixture isdetermined (88.4% minimum). The heat is removed; 280 parts of M-pyrolare added and the mixture is allowed to cool. The resulting product hasZ₇ viscosity at 80.0% solids.

EXAMPLE 4

A hydroxy functional epoxy-polyester graft copolymer was preparedaccording to the invention. In a suitable reactor were charged 608 partsEpon 829 (trademark; Shell Chemical Company; diepoxide resin), 167 gramsbisphenol A, 225 parts PCP-0200 (trademark; Union Carbide; an aliphaticdiol, specifically, polycaprolactone diol), and 90 parts xylene. Themixture was brought to reflux; a partial vacuum was applied to removethe xylene and residual water. 2 parts benzyl dimethyl amine are addedand the mixture was raised to 160° C. The mixture was reacted to G-Hviscosity (tested as 15 parts mixture and 15 parts cellosolve yielding a50.0% solids solution). The mixture was then cooled to 120° C., and 2.0parts of benzyl dimethyl amine were added. The progress of the reactionis followed by viscosity measurement. After 2 hours the viscosity wasdetermined to be P-Q (tested as 20 parts mixture and 20 parts cellosolveyielding a 50% solids solution). Then 88 parts diethanolamine and 242parts Solvesso 150 (trademark; Shell Chemical Company; aromatic solvent)were added to the mixture and the temperature raised to 160° C. forabout 1 hour. Subsequently, 1088 parts epsilon-caprolactone and 1.0 partmonobutyl tin anhydride were added to the mixture and the temperaturewas brought up to 130° C. at which point a mild exotherm occurred whichraised the temperature to 170° C. After 2 hours the reaction wasstopped, heating was removed and 272 parts M-pyrol was added; themixture was allowed to cool. The resulting product had a Z₇ viscosity at80.0% solids.

EXAMPLE 5 Preparation of Blocked Polyisocyanate Crosslinking Agent

Into a suitable reactor were charged 870 parts methylethyl ketoxime and180 parts Solvesso 100. 1330 parts of PAPI 27 (trademark; UpjohnChemical Company; aromatic polyisocyanate) was added dropwise to themixture over two hours and the reaction temperature increasses from roomtemperature to 80°-95° C. 39 parts 2-ethylhexanol was added to themixture and the temperature of the mixture was maintained at 85°-95° C.for one hour. At that point, 516 parts of M-pyrol was added and themixture was cooled. The resulting resin was dark brown and had aviscosity of 6000 cps at 75.0% solids.

EXAMPLE 6 Preparation of Blocked Polyisocyanate Crosslinking Agent

Into a suitable reactor were charged 537 parts methylethyl ketoxime. 784parts PAPI 94 (trademark; Upjohn Chemical Company; aromaticpolyisocyanate) was added dropwise over two hours; the reactiontemperature rose from room temperature to 85°-95° C. After 30 minutes,the mixture was checked to insure complete reaction of the isocyanate byinfrared spectroscopy. If residual isocyanate was detected, additionalmethylethyl ketoxime was added to the mixture. Subsequently, 300 partsmethylamyl ketone and 150 parts M pyrol were added and the mixture wascooled.

EXAMPLES 7-10 Preparation of Blocked Polyisocyanate Crosslinking Agent

Blocked isocyanate crosslinkers were prepared in the manner of Example6. The components employed are shown in the table below.

    ______________________________________                                                     Example                                                                       7    8         9       10                                        Composition    Parts                                                          ______________________________________                                        L-2991 A*      360    360       360                                           Desmodur IL*                          525                                     methyl ethyl ketoxime                                                                        174                     87                                     benzotriazole         238                                                     epsilon-caprolactam             227                                           N--methyl pyrolidone                                                                         133    150       195   461                                     Percent non-volatiles                                                                         80    80.1      75.1   57                                     Viscosity      Z.sub.1                                                                              Z.sub.6   Z.sub.2                                                                             Z                                       ______________________________________                                         *Trademarks of Mobay Chemical Co.; L229l A is a biurette of hexamethylene     diisocyanate; Desmodur IL is a polyisocyanurate of tolylene diisocyanate.

EXAMPLE 11 Millbase Preparation

In a one gallon can or ballmill are charged the following materials andone quart of diagonal shot. The mixture is placed on a roller mill for16-24 hours to reach a 7+ hegman dispersion. At that point, the letdownis added, and the mixture is run an additional hour on the roller mill.

    ______________________________________                                                              Parts                                                   ______________________________________                                        Hi-Sol #3*              585                                                   2-Ethyl Hexanol         95                                                    Polyethylene Wax        70                                                    Anti-Terra-U**          40                                                    Resin of Example 1      103                                                   Barytes                 2259                                                  TiO.sub.2               429                                                   Carbon Black            29                                                    Strontium Chromate      143                                                   Letdown:                                                                      Resin of Example 1      247                                                   ______________________________________                                         *Trademark of Ashland Chemical Co., Columbus, Ohio; HiSol #3 is an            aromatic solvent.                                                             **Trademark of Byk Mallinckrodt, Wallingford, CT 06492; AntiTerra-U is an     antisettling and wetting agent.                                          

EXAMPLE 12 Bentone Gel Preparation

To a clean Ball Mill are charged the following:

    ______________________________________                                                                 Parts                                                ______________________________________                                        Solvesso 150*              513                                                Propylene Carbonate        13                                                 Bentone 38**               30                                                 After grinding for         384                                                30 minutes is added:                                                          Resin of Example 1                                                            Grinding for approximately 2 hours                                                                       60                                                 yields an 8 Hegman dispersion. At                                             that point the letdown is added:                                              Hi-Sol #3                                                                                                1000                                               ______________________________________                                    

EXAMPLES 13-15

Coating compositions according to the present invention are preparedaccording to the following formulations.

    ______________________________________                                        Coating Compositions                                                                          Example                                                                       13      14     15                                             Composition       Parts                                                       ______________________________________                                        Resin of Example 4                                                                              2241      2241                                              Resin of Example 3                 2241                                       Millbase of Example 11                                                                          5788      5788   5788                                       Bentone Gel of Example 12                                                                       2315      2315   2315                                       Crosslinker of Example 5                                                                         984              984                                       Crosslinker of Example 6    1050                                              Dislon*            114       120    120                                       Cab-O-sil**        142                                                        ______________________________________                                         *Trademark; Kusumoto Chemicals, Ltd.; antisettling agent to control the       thixotropic properties of the composition                                     **Trademark; Cabot Corporation; antisettling agent to control the             thixotropic properties of the composition.                               

The coating compositions are prepared by sequential mixing in a 5 gallonworking capacity EMCO Proto-Lab SW Mill (trademark), Epworth Mfg. Co.,South Haven, Mich., set at 900 rpm. Resin and Dislon are first mixed forapproximately 10 minutes and then millbase, Bentone gel and crosslinkerare added sequentially while mixing. Finally, Cab-O-Sil is added and thecomposition mixed until a grind of 6⁺ on the Hegman scale is obtained.

The resulting compositions each is sprayed at 140°-160° C. usinghot-spray equipment commercially available from Nordson Corp. UnpolishedBonderite steel panels are sprayed and baked at 135° C. for 20 minutes.The thickness of the coating tested varies from 5 mils to 12 mils. Thepanels are top-coated with white enamel and tested for chip resistanceusing 10 pts. of gravel in the gravelometer test. All the abovecompositions exhibit excellent chip resistance. In addition, the panelsshow excellent corrosion resistance (500 hrs. salt spray test, scribedpanels) and humidity resistance.

EXAMPLES 16-19

Additional coating compositions according to the invention are madeaccording to the method of Examples 13-15 and according to the followingformulations.

    ______________________________________                                                       Example                                                                       16   17       18     19                                        Composition      Parts                                                        ______________________________________                                        Resin of Example 4                                                                             2241   2241     2241 2241                                    Millbase of Example 11                                                                         5788   5788     5788 5788                                    Bentone Gel of Example 12                                                                      2315   2315     2315 2315                                    Crosslinker of Example 7                                                                        922                                                         Crosslinker of Example 8                                                                               922                                                  Crosslinker of Example 9          984                                         Crosslinker of Example 10             1294                                    Dislon*           100    100      100  100                                    ______________________________________                                         *Trademark; Kusumoto Chemicals, Ltd.; antisettling agent to control the       thixotropic properties of the composition.                               

Coatings on motor vehicle body panels, made from the compositions ofExamples 16-19 are found to provide good corrosion protection and goodprotection against stone chipping and the like.

Many modifications of this invention will be apparent, in view of thisdisclosure, to those skilled in the art. It is intended that all suchapparent modifications fall within the true scope of this invention andbe included within the terms of the appended claims.

Industrial Application

It will be apparent from the foregoing that this invention hasindustrial applicability as a coating composition, especially as a hotsprayable, high solids coating composition suitable for use as a chipresistant automotive vehicle primer adapted for use on body panel areassubject to chipping by stones, gravel and other road debris.

What is claimed is:
 1. A hydroxy functional epoxy-polyester graftcopolymer suitable for use in a thermosetting composition, whichcopolymer has a number average molecular weight (M_(n)) of between about2,000 and about 20,000, said copolymer being the product ofpolymerization of lactone monomers in the presence of hydroxy functionalepoxy amine adduct precursor having a number average molecular weight(M_(n)) of between about 1,000 and about 4,000, said precursor being thereaction product of diepoxide with aliphatic diol in chain extensionreaction and hydroxy functional secondary amine in chain terminationreaction in approximately a 1 to 1 equivalent ratio with the chainextended reaction product, wherein said polymerization of said lactonemonomers is carried out at a temperature between about 50° C. and about300° C. and the polymerization reaction mixture comprises between about10 and about 80 weight percent said hydroxy functional epoxy ester resinprecursor and between about 90 and about 20 weight percent said lactonemonomers.
 2. The hydroxy functional epoxy-polyester graft copolymer inaccordance with claim 1, wherein said diepoxide is selected from thegroup consisting of bisphenol-A epichlorohydrin epoxy resin, hydantoinepoxy resin, cyclic and acylic aliphatic diepoxides, and a compatiblemixture of any of them.
 3. The hydroxy functional epoxy-polyester graftcopolymer in accordance with claim 1, wherein said aliphatic diolreactant has the general formula:

    HO--R--OH

wherein R is a divalent, aliphatic, linking moiety substantiallyunreactive with said diepoxide.
 4. The hydroxy functionalepoxy-polyester graft copolymer of claim 1, wherein said diol has amolecular weight of about 60-500 and is selected from the groupconsisting of alkyl substituted or unsubstituted propanediol,butanediol, pentanediol, hexanediol, and a mixture of any of them. 5.The hydroxy functional epoxy-polyester graft copolymer of claim 1,wherein said aliphatic diol bears two terminal hydroxy functionality. 6.A solvent based, thermosetting coating composition in accordance withclaim 1, wherein said hydroxy functional secondary amine has the generalformula: ##STR8## wherein R' and R" are selected from aliphatic,cycloaliphatic and aromatic radicals which will not interfere with thechain termination reaction of the diepoxide and the hydroxy functionalsecondary amine to form the hydroxy functional epoxy amine adduct, andwherein X is selected from the group consisting of hydrogen and hydroxylradical.
 7. A solvent based, thermosetting coating composition inaccordance with claim 6, wherein said hydroxy functional secondary aminebears primary hydroxyl functionality.
 8. A solvent based, thermosettingcoating composition in accordance with claim 7, wherein said hydroxyfunctional secondary amine is selected from the group consisting ofdiethanolamine, methylethanolamine, dipropanolamine andmethylpropanolamine.
 9. The hydroxy functional epoxy-polyester graftcopolymer in accordance with claim 1, wherein said lactone monomers areselected from those represented by the general formula: ##STR9## inwhich n is at least 4, at least n+2 R's are hydrogen, and the remainingR's are substituents selected from the group consisting of alkyl,cycloalkyl, alkoxy and single ring aromatic hydrocarbon radicals. 10.The hydroxy functional epoxy-polyester graft copolymer in accordancewith claim 9, wherein said epsilon-caprolactone monomers compriseunsubstituted epsilon-caprolactone monomers.